I wasn't concerned so much with the aggression as I was with the idea that corys do better in groups of 5 and didn't know if the others being a slightly different cory if they would group together or not.
When I initially bought them someone at the lfs
told me three would be fine, but I learned here 5 is the magic number so I wanted to get 2 or 3 more
"There's always a bigger fish." - Qui-Gon Ginn